We have previously discovered that over-expression of glial cell line-derived neurotrophic factor (GDNF) via adeno-associated virus (rAAV) in the nigrostriatal tract in leads to highly significant weight loss in intact aged obese rats, middle aged rats, and lack of weight gain in young rats. Moreover, GDNF over-expression in striatal terminal fields has no significant effect on weight gain. To date, we have traced the effect of nigral over-expressed GDNF to the paraventricular nucleus of the hypothalamus. However, when GDNF is over-expressed directly in hypothalamus at levels equal to those achieved with nigral rAAV-GDNF, the animals lose less weight. These data may suggest that nigral GDNF over-expression is having effects in nuclei outside just the hypothalamus. The present proposal is designed to determine the extent to which the mesolimbic dopamine (DA) projection from the ventral tegmental area (VTA) to the nucleus accumbens (nAcc) contributes to GDNF-over-expression induced weight loss. We have preliminary data indicating that injections of recombinant adeno-associated viral vector (rAAV)-GDNF in VTA also leads to weight loss in rats. Thus, far, no effect of GDNF on DA levels or turnover has been related to GDNF over-expression has been observed but this does not conclusively rule out DA as an important mediator of GDNF over-expression induced weight loss. Aim 1 is designed to determine if the terminal field of the mesolimbic DA projection, the nAcc or the VTA itself is the site of action of rAAV-mediated GDNF over-expression induced weight loss. Secondarily, we will determine if co-expression in the nigrostriatal tract and the mesolimbic DA projection produces an additive effect on body weight. Aim 2 is designed to determine the extent to which mesolimbic DA plays a direct role in GDNF-over-expression induced weight loss. We will take care to determine if our animals are hyperactive, have increased oxygen utilization, or display anxiety-like behaviors to determine potential behavioral effects of GDNF over-expression that may account for the observed weight loss. We will also measure serum and CSF levels of hypothalamic-pituitary-adrenal (HPA) axis hormones and downstream signaling molecules to try to fully characterize the HPA response to GDNF over-expression.

Public Health Relevance

This project is aimed at following up on the novel discovery from the Mandel laboratory showing that if glial cell line-derived neurotrophic factor (GDNF) is over-expressed in the dopamine cells of the nigrostriatal tract, rats of varying ages and metabolic function all lose weight (middle aged- aged obese rats) or fail to gain weight (younger rats). A series of experiments are proposed to look at which anatomical structures contribute to this important novel effect and to determine if dopamine is required to observe GDNF-induced weight loss.